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Advance Adapters Jeep Wrangler Rubicrawler Kit - Double Down

Posted in How To: Transmission Drivetrain on January 1, 2010
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Photographers: David Hamilton

For years we've begged the engineers at Jeep to offer a three-speed transfer case.

The 4:1 Rock-Trac T-case is great and all, but really only in the rocks or through technical sections. It's pretty much worthless in the mud and sand where more wheelspeed is needed. Several aftermarket options have been available for many years; however all of them have required extensive modifications and new driveshafts, until now. The people at Advance Adapters did their homework and discovered that the tailhousing in the 42RLE automatic transmission found in '03-'09 Wranglers is simply an empty case. With a little ingenuity a heavy-duty six-pinion 2.72:1 low-range planetary gearbox was stuffed into this dead wasted space between the transmission and stock transfer case. The RubiCrawler was born. The result is a compact bolt-in gearbox that allows more gearing versatility than the stock 4:1 found in Rubicons and the necessary double-deep gearing that the non-Rubicon models require for the rocks. It's a win-win for everybody.

How's It Work?
Since the install, our RubiCrawler-equipped '07 Wrangler Rubicon has crawled the Rubicon Trail, revved through the Pismo sand dunes, and commuted several thousand miles on the highway. It shifts smoothly and easily and doesn't make any unusual noises. If you can shift the stock transfer case, you can easily shift the RubiCrawler without issue.

In the rocks, the stock 4:1 low-range transfer case gearing compounded with the RubiCrawler's 2.72:1 provides a whopping 10.88:1 low range ratio. On paper it seems like way too much, but it turned out to be extremely helpful in really tight situations where it helped us avoid body damage. The slower speed provided better throttle control and less bobbing over the rough stuff.

In the dunes we found the RubiCrawler's 2.72:1 way more useful than the factory 4:1 low range. We could blast up dunes in 4Hi with the RubiCrawler engaged and the rear locker on. We also liked running the 2.72:1 RubiCrawler with the T-case in 2Hi and the rear locker on. In the past the Jeep would sort of bog in High range or simply over-rev in Low. The RubiCrawler puts the gearing in the middle for optimum performance. Overall, the addition of the RubiCrawler makes the Wrangler Rubicon more versatile and perform better in every terrain.

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Advance Adapters
Paso Robles, CA 93446

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